well, the question is if that is a matter best left unanswered. yes the master has more than enough power to do that, (i will admit that possibility crossed my mind very early on the first build, given furry erotica dives pretty deep on fetishisation at times), but they also often despised him as a mere beast. in that sense while a master may not have had any regards from abusing Asterion, it is still possible the thought never crossed their minds. but it is also a very unconfortable topic that can easily backfire were it to be elaborated on, with that thought it may be for the best to leave it as a mere implication instead of actually saying it, as often is done with potentially triggering material that while it fits naturally with the story, people wouldn't necessarily be okay with seeing that play out at all. reading the comments around here should be pretty easy to find people who aren't willing to read the ruthless route for example, and that's arguably tame if you ask me.
I'm not saying that the current master should abuse Asterion (definitely not), or that the Devs should give a detailed look into what that abuse entails (from previous masters, if it existed at all). I only wanted to address the possibility that it may have happened in the past, and if it has happened that it should at least be touched upon during the psychological therapy portions with Asterion (assuming they add that to the game, which I think they should).
I really don't want a graphic blow by blow depiction of any abuse towards Asterion, certainly not sexual abuse, but I think that (again IF it has occurred with past masters) it should be directly looked at during those therapy sessions. It seems unrealistic to just ignore what would undoubtedly be a very traumatic incident (or series of incidents) for Asterion, when the purpose of the therapy is to acknowledge the past forms of abuse enacted against him, and help him to move forward, and hopefully begin to heal some of his psychological trauma.